Two equipment replacement models are reviewed, revised, and compared. The advantages and disadvantages of each is outlined. A generalization of the model presented by Tufts and Mills (1982) was found to properly incorporate all costs associated with equipment replacement. A revised Butler and Dykstra (1981) model was still found to incorrectly estimate capital investment costs. Butler and Dykstra's simpler procedures for estimating some of the costs needed in both models could reduce the difficulty of implementing the Tufts and Mills model. The Tufts and Mills model is flexible and is applicable to other management decisions. Forest Sci. 31:661-670.